The Nature of Sound

Section 2:

Properties of Sound

Essential Questions

How does the speed of sound differ in different media?

How are frequency and pitch related?

What is the Doppler Effect?

How are amplitude and loudness related?

How can frequency and amplitude be “seen” on an oscilloscope?

Vocabulary

Pitch – depends on frequency of the sound wave; measures how high or low a sound is perceived

Doppler Effect – change in frequency of a sound wave when the source or observer is moving

Loudness – extent to which a sound can be heard

Decibel – the most common unit to measure loudness: symbol is dB

The Speed of Sound

Speed of sound depends on its’ medium

• Sound travels fastest in solids, second fastest in liquids, and more slowly through air

Temperature also effects the speed of sound

• The cooler the medium, the slower the sound

Pitch and Frequency

Pitch – how high or low a sound seems

Frequency – the number of crests or troughs in a given time

• Expressed in hertz (Hz): 1 Hz = 1 wave/second

Pitch and frequency are related

Sounds that have a frequency too high for people to hear are called ultrasonic

The Doppler Effect

The Doppler effect is the apparent change in frequency of a sound caused by the motion of the listener or the source

Movement causes the compressions and rarefactions to be closer together or further apart; this is why the frequency and pitch change

Loudness and Amplitude Loudness is a measure of how well a

sound can be heard

• More energy = larger vibrations = louder sounds

Increasing energy increases amplitude

• Amplitude of a wave is the largest distance particles vibrate from the rest position

• Larger amplitude = louder sound

• Smaller amplitude = smaller sound

Measuring Sound

Unit used to express loudness is the decibel (dB)

Oscilloscope – graphic representations of sound waves